There is known an image forming device, such as a printer, a fax, a copier, a plotter or a multi-function peripheral having multiple image forming functions (including print, fax, copy, and the like functions), which uses a liquid discharge mechanism. The liquid discharge mechanism includes a recording head in which liquid discharge heads for discharging drops of recording liquid are arranged. With this recording head, image formation (which is inclusive of image recording and printing) is carried out by discharging drops of the recording fluid (ink) to a medium (recording sheet) while the medium (recording sheet) is transported.
An image forming device hereinafter refers to a device which performs image formation by discharging liquid drops to a medium (which is inclusive of paper, yarns, fibers, textile, leather, metal, plastics, glass, wood, ceramics, etc.). Image formation hereinafter refers to not only formation of images with meaningful characters, figures, etc. but also formation of images with meaningless patterns, etc. Liquid hereinafter is not restricted to a recording fluid or ink, but refers to any fluid which is a liquid state when it is discharged. A liquid discharge device hereinafter refers to a device in which a liquid discharge head discharges liquid drops, and it is not limited to a device which performs image formation.
The image forming devices provided with liquid discharge heads are classified into two types: a serial type image forming device in which a recording head provided on a carriage is moved in a main scanning direction perpendicular to a sheet transport direction to perform recording or printing; and a full-line type image forming device which uses a full-line type recording head in which a plurality of ejection holes (nozzles) for discharging liquid drops are arranged to cover the overall recording region.
A liquid discharge head for use in an image forming device is arranged to discharge liquid drops from ejection holes in order to perform recording or printing. If a non-discharge state of the liquid discharge head keeps on for a certain period, the viscosity of the liquid in the ejection holes is increased by evaporation of the solvent, etc. If the discharge operation is started from the non-discharge state, the discharging state of the head is disturbed with the increased viscosity and the liquid discharge head will be inoperable and the printing quality will deteriorate. To avoid this, idle discharge operation in which liquid drops (waste fluid) that are not used for image formation are discharged from the nozzles is performed and the recording fluid remaining in the nozzles with the viscosity increased is eliminated.
Regarding idle discharge operation, Japanese Laid-Open Patent Application No. 11-105304 discloses an ink jet printer in which an ink jet head is provided with a preliminary discharge unit which performs preliminary discharging of ink for preventing clogging of the nozzles in the ink jet head, in a position separated from a recording medium during the scanning of the ink jet head on the recording medium.
Japanese Laid-Open Patent Application No. 2001-026123 discloses an ink jet recorder in which data for ejecting flushing dots from a nozzle for ejecting a small amount of ink is generated based on print data for one path. A head driving unit performs a printing operation in accordance with the data wherein printing dots as well as flushing dots smaller than the printing dots are ejected to a recording medium during the scanning of a carriage. As a result, the flushing dots are suitably ejected from the small-amount ejecting nozzle during the period of one path as needed, and it is possible to assure that the normal printing operation is performed even by a recorder using a comparatively large sized recording medium. Moreover, Japanese Laid-Open Patent Application No. 2005-313624 discloses a liquid discharge head which performs a preliminary discharge operation during a normal printing operation.
Japanese Laid-Open Patent Application No. 2005-007899 discloses a full-line ink-jet recording device in which an idle discharge region for performing idle discharge of liquid drop is set up in a position separated from a recording region. An idle discharge recording liquid portion for receiving the liquid drops when idle discharge is performed is arranged in the idle discharge region. A recording head unit including a full-line ink jet head is moved or rotated to the idle discharge region, and it is caused to perform idle discharge operation. Thereafter, the recording head unit is returned to the recording region by performing a head returning operation.
Moreover, Japanese Laid-Open Patent Application No. 2001-105589 discloses a method of driving a liquid discharge head. Japanese Laid-Open Patent Application No. 2002-248766 discloses an image forming device which uses an ink in which charged particles are distributed in a solvent.
However, it is difficult to apply the idle discharge method which performs idle discharge (preliminary discharge) operation in a position separated from the recording medium during the print scanning, according to Japanese Laid-Open Patent Application No. 11-105304, to the full-line type image forming device in which the recording head is moved. Even if the application of the idle discharge method mentioned above is possible, the problem that the printing speed in such a case extremely falls remains unresolved.
The idle discharge method which generates the data for idle discharge (flushing) based on the print data for one path and performs idle discharge within one print path, according to Japanese Laid-Open Patent Application No. 2001-026123 and others, would require the analysis of data with little ink discharge, the generation of the data for idle discharge according to image data, and the switching of the drive circuits which generate a drive waveform for normal printing and a drive waveform for idle discharge. Therefore, the problem that the processing is complicated and the cost is increased remains unresolved.